
/**
 * Handles toggling the navigation menu for small screens.
 */
(function() {
    var button = document.getElementById('topnav').getElementsByTagName('div')[0],
            menu = document.getElementById('topnav').getElementsByTagName('ul')[0];

    if (undefined === button)
        return false;

    // Hide button if menu is missing or empty.
    if (undefined === menu || !menu.childNodes.length) {
        button.style.display = 'none';
        return false;
    }

    button.onclick = function() {
        if (-1 == menu.className.indexOf('srt-menu'))
            menu.className = 'srt-menu';

        if (-1 != button.className.indexOf('toggled-on')) {
            button.className = button.className.replace(' toggled-on', '');
            menu.className = menu.className.replace(' toggled-on', '');
        } else {
            button.className += ' toggled-on';
            menu.className += ' toggled-on';
        }
    };
})();
